This invention relates to the production of a high purity iron sulfate monohydrate and a separate concentrated sulfide residue containing valuable metals from complex sulfide ores and concentrates containing iron sulfide minerals and non-ferrous metals of significant value.
It is particularly suited to the treatment of iron sulfide ores containing base metal sulfides which because of their complex mineralogy or relatively fine grain size distribution do not lend themselves to economic processing by conventional methods of separation and beneficiation for the selective recovery of the valuable metals they contain.
It has, furthermore, the important advantage of recovering a substantial part of the iron sulfides sulfur in the form of hydrogen sulfide. Thus it lends itself to the adoption of pollution free flow-sheets for the complete separation and recovery of all of the valuable constituents of the sulfide ores or concentrates, including both iron and base metals while all of the sulfur can be recovered as elemental sulfur, which is the form under which it can be marketed most easily.
Prior art processes for the production of iron sulfate, generally have used available supplies of industrial wastes such as the acidic effluent from coal, steel, and pigment production, as feed materials, and generally have operated primarily as waste disposal processes. Most of these processes are not capable of extracting iron from iron bearing sulfide minerals.
Essentially, in all of them, non-ferrous impurities remain with the iron products recovered, thus adversely affecting their quality and reducing their value for use in the production of steel. Furthermore, these processes tend to consume excessive quantities of fuel to dehydrate the iron sulfate. This results in prohibitive costs for the products obtained, which cannot be marketed profitably. Under present conditions, the use of these processes would result in commercial losses and would only be justified on the basis of waste disposal considerations.
The prior art process of U.S. Pat. No. 3,053,651 is capable of extracting and recovering iron both from iron bearing sulfide minerals, and from waste liquors containing iron sulfate and sulfuric acid. This process also provides for purification of the solution, and the iron sulfate product. However, partially soluble sulfides of metals like zinc and/or nickel frequently are present in available feed materials, and this patent does not disclose any process for the removal of such metals from the iron sulfate solution. When present, these base metal impurities would accumulate in iron sulfate crystals, if not removed, and would generally render the iron sulfate products unacceptable as a source of iron oxide for use in the production of steel.
The above process, in common with other prior processes for the production of iron sulfate, discloses the use of commercial fuel as the source of heat to separate the water from the iron sulfate. This would require excessive quantities of fuel because of the large amounts of water to be removed, resulting in excessive operating costs.